Method and device for monitoring electric components in a pick-and-palce device for substrates

ABSTRACT

The invention relates to a method and to a device for monitoring electric components in a pick and place device for substrates. The underside of a pick-up ( 2 ) is monitored by an optical scanning means ( 7 ) during the pick-up phase and during the placing phase of a component ( 10 ). A lift drive ( 3 ) for the pick-up ( 2 ) is provided with a position sensor ( 5 ) that is linked with a control device ( 6 ). The scanning means ( 7 ) emits and receives a scanning beam ( 22 ) oriented transversally to the direction of lift and is likewise coupled with the control device ( 6 ), thereby allowing to monitor the underside of the pick-up ( 2 ) in a direct time-related manner with the picking and placing of the component ( 10 ). The various lift positions are saved and compared when a threshold value of the received scanning beam ( 22 ) is exceeded so that the inventive device also allows for a monitoring of the height of the component.

[0001] The invention relates to a method and a device for checkingelectric components in a pick-and-place device for substrates,

[0002] the components being handled by a pick-and-place head of thepick-and-place device which is made to travel in a working plane,

[0003] a pick-up for the components being displaced in thepick-and-place head perpendicularly in relation to the working plane bymeans of a lift drive between a transporting position and a functioningposition,

[0004] the component being sucked against an underside of the pick-up,

[0005] the component being raised by the pick-up from a pick-up positioninto the transporting position and, after the pick-and-place head hasbeen made to travel into a placement position, is lowered onto thesubstrate into the functioning position, and

[0006] the positional relationship between the component and the pick-upbeing checked by an optical scanning means of the pick-and-place head.The positional relationship is to be understood here as meaning not onlythe relative position of the components on the pick-up, but also thepresence or absence of the component on the pick-up.

[0007] A device of this type is disclosed by U..S Pat. No. 5,660,519.According to the latter, the scanning means of the pick-and-place headin each case comprises a row of transmitting and receiving diodes, whichform a scanning plane perpendicular to the lifting direction at theheight of the component located in the transporting position. While thepick-and-place head is traveling to the placement location on thesubstrate, the side contours of the component can be scanned by rotatingthe suction pick-up about the lifting axis, which allows the positionaldeviation of the center of the component from the pick-up axis to beascertained. The presence or absence of the component on the pick-up isdetected during the picking-up or placing of the component by sensingthe suction pressure at the pipette. It goes without saying that thepresence or absence of the component can also be established by opticalmeasurement.

[0008] Furthermore, JP 11-154797 A discloses a pick-and-place devicewith a fixed turntable rotating step by step, under which a printedcircuit board can be made to travel in two coordinate directions. Theturret-like turntable is equipped with a multiplicity of pick-ups forthe components, which run step by step through different stations andwhich transport the components from a pick-up position to an oppositeplacement position. Before the picking-up, the free end of the pick-upruns through a control station with a perpendicular row of opticaltransmitting and receiving diodes in the manner of light barriers,whereby the position in height of the underside of the pick-up can beascertained. After the picking-up of the component, the end of thepick-up with the component runs through a further optical controlstation with a perpendicular row of diodes, whereby the position inheight of the underside of the component, and consequently its overallheight, can be ascertained. In the case of a pick-and-place head whichcan be made to travel in two coordinate directions, the pick-up wouldhave to run through the fixed control station before and after pickingup the component to allow a corresponding measurement to be carried out,which would generally involve an unacceptable detour between the pick-upposition and the and the placement position, and vice versa.

[0009] Furthermore, it is known, for example from U.S. Pat. No.4,875,285, to design the pick-and-place head in the manner of a turretwith a multiplicity of suction pick-ups arranged in a circular manner ona rotor, a stator having with processing stations for the componentsarranged along the circulatory path of the pick-ups, which componentsare centered, contacted and electrically, optically or mechanicallymeasured in these stations, for example according to column 2, line 65et seq. It is currently generally customary to carry out the positionaldetermination of the components on the pick-up by means of a CCT camera,which measures the placement side of the components, in particular theposition of the contact areas, in reflected light. The angular positionof the component can be corrected in a downstream rotating station. Thex-y offset is taken into account by corresponding correction of thetarget coordinates of the pick-and-place head.

[0010] Furthermore, WO 9949713 A discloses a turret pick-and-place headwith a stator and a rotor, which is provided with pick-ups for thecomponents arranged in a circulatory manner. A line sensor is arrangedon the stator outside a lower placement station between two holdingstations for the pick-ups into the and aligned in relation to the axisof rotation of the rotor. The components sliding past, adhering to thepick-up, can be identified from the obscuration of the sensor. Since thepick-up has to be moved into the sensing range of the sensor, it cannotbe checked in a direct time-related manner with the picking-upoperation. Since the light directed onto the line sensor cannot beexactly focused, adequately sharp projection is not possible, inparticular for highly miniaturized components. Sharp optical focusing ispossible only in the case of a singular scanning beam, for example of alaser light barrier.

[0011] The current trend toward ever smaller components, of for examplean edge length of 0.25 mm, requires a very narrow suction channel in thepick-up, which makes it difficult for the vacuum to be sensed, inparticular when there is soiling. Furthermore, inaccuracies of thepick-up position may occur if the component does not completely coverthe suction channel and, as a result of this leakage, the result of thevacuum scanning is unreliable. For example, in the case of a turrethead, under some circumstances the absence of a component isconsequently only noticed in the optics station during the placementphase. The picking up of a replacement component requires a considerableadditional amount of time to be expended.

[0012] The invention is based on the object of achieving a higher levelof reliability in the checking of the components.

[0013] This object is achieved by the invention as claimed in claim 1.For example, the optically precisley focusable scanning beam, forexample of a laser diode, may be arranged just underneath the undersideof the pick-up in the raised state. This makes it possible to check theunderside of the pick-up before it is lowered onto the component to bepicked up. Normally, the path of rays of the light barrier is notinterrupted. After that, the pick-up is lowered onto the component to bepicked up. The latter is then sucked onto said pick-up and raised.Directly after that, it can be reliably established by a renewedscanning pulse whether the component has been picked up by the pick-up.If there is exact focusing of the scanning beam, it is possible to keepthe free distance between the transmitting means and receiving meansparticularly large, so that even extremely large components can bepassed through and that the light barrier can be used for example evenin a turret pick-and-place head, where it is not possible to get closeto the component on account of the complex form of construction.

[0014] It is customary practice for the components to be supplied inbelt pockets. When the belt is advanced, it may happen that vibrationscause the component to come out of the pocket or change its position,but it is also possible on account of the tolerances mentioned for thepick-up not to pick up the component. The directly following scanningcan immediately initiate a new picking-up operation, in which the beltis advanced by a further pocket spacing, so that the pick-up can pick upanother component. This takes place without any further travelingmovement of the pick-and-place head and consequently with little timedelay.

[0015] Directly before the component is placed onto the substrate,scanning may be carried out once again, in order to establish whetherthe component is still present on the pick-up. This is advantageous ifthe component is lost before it is placed, for example as a result ofvibrations, accelerations or decelerations of the pick-and-place head.In this case, the setting down of the pick-up is not performed. This isof significance to the extent that otherwise the underside of thepick-up would be set down onto the soldering paste present on theprinted circuit board, with the effect of contaminating the underside somuch that the suction opening is considerably narrowed or even closed.If the component is present, it is placed onto the substrate andreleased from the underside by means of a pulse of compressed air. Inthe case of very small components, however, the adhesive action of acontaminated underside may be to so great that the component sticks tothe pick-up. This is established by scanning directly after the raisingof the pick-up, so that the pick-up can once again attempt to place thecomponent onto the substrate before the pick-and-place head leaves theplacement position. In this way, a high degree of picking and placingreliability is achieved.

[0016] Complete monitoring of the underside of the pipettes in alloperating phases is achieved by an advantageous development of theinvention as claimed in claim 2.

[0017] It is possible by the development as claimed in claim 3 not onlyto check the presence of a component but also to ascertain the height ofthe component, allowing additional information to be obtained concerningthe type of component. For example, it may happen that the componentlying in the belt pocket is sucked against the pick-up one-sidedly, sothat it is picked up on edge by the pick-up. With the aid of the exactlyfocused scanning beam, this can be detected already during picking-up asa pick-up error even in the case of the highly miniaturized componentsthat are especially susceptible to this. Such a component is discardedin a specific position and consequently does not get onto the substratein an undefined way. It is particularly advantageous to measure the tipof the pick-up in each case during the upward movement following theplacement of a component and after the pick-up of the followingcomponent, since the hysteresis of the displacement-measuring systemdoes not occur when the direction of movement is the same.

[0018] The device as claimed in claim 4 achieves the object on which theinvention is based in a way similar to the method according to FIG. 1.Here, too, the conditions on the underside of the pick-up can becompletely monitored, so that the level of pick-and-place reliability iscorrespondingly increased.

[0019] In a way similar to the method as claimed in claim 3, the deviceas claimed in claim 5 permits more accurate checking of the componentheight in the lifting direction, from which more accurate conclusionscan be drawn concerning the type or the installation position of thecomponent.

[0020] It is possible by the device as claimed in claim 6 for thescanning means to be combined in a structure, whereby an exactgeometrical relationship between the functional parts can beestablished. The deflecting means near the underside can be formed forexample by a prism which deflects the scanning beam obliquely upward toa transmitting diode.

[0021] The turret pick-and-place head as claimed in claim 7 has, forexample, 12 suction pick-ups, which are arranged in a star-shaped manneralong a circular circulatory path. The rotor is driven step by step, sothat the suction pick-ups can be rotated one after the other into thepick-up station, in order to be able to pick up the components in adirect sequence. However, this means that, before they can be opticallyinspected, the components run through at least several stations, untilthey reach an optics station. In this period of time, it is not possiblewithout the scanning means according to the invention for the componentsto be optically checked. Some of the components are only taken past theoptics station and checked in the placement phase. As a result, pick-uperrors which cannot be detected by the vacuum sensing are only detectedin a later phase

[0022]FIG. 7 shows the parts according to FIG. 6 after the end of thepick-up phase,

[0023]FIG. 8 shows the parts according to FIG. 7 during a placementphase of the component onto a substrate,

[0024]FIG. 9 shows the parts according to FIG. 9 after the placement ofthe component,

[0025]FIG. 10 shows a side view of another, turret-like pick-and-placehead with components and a substrate,

[0026]FIG. 11 shows a side view of the parts according to FIG. 10.

[0027] According to FIG. 1, a pick-and-place head 1 which can be made totravel in two coordinate directions X and Y of a horizontal workingplane X-Y is provided with a pick-up 2, which is displaceable by meansof its lift drive 3 perpendicularly in relation to the working plane.The pick-up 2 is provided on its downwardly pointing tip with a suctionopening 4 for workpieces to be picked up. The lift drive 3 has adisplacement-measuring means 5, with which the respective liftingposition of the pick-up can be established and which is connected via adata line to a control means 6 of the pick-and-place device. In theregion of the underside of the pick-up 2 there is fastened to thepick-and-place head 1 a scanning means 7 in the form of a forked lightbarrier, which is provided with a transmitting diode 8 and a receivingdiode 9. The diodes are arranged and aligned with each other in such away that a sharply focused scanning beam 22 running between them crossesthe pick-up axis perpendicularly. The scanning means 7 is likewiseconnected to the control means 6 via a further data line.

[0028] In the transporting position shown, the pick-up 2 is in theuppermost lifting position, in which the underside of the pick-up 2 islocated above the scanning height defined by the diodes. The controlmeans 6 receives the measured displacement values of thedisplacement-measuring means 5. The scanning means is activated duringthe lowering and lifting phases of the pick-up 2. The signals receivedby the receiving diode are likewise transmitted to the control means 6.At the moment at which the received brightness value of the receivingdiode 9 exceeds a threshold value, the lifting displacement justmeasured of the pick-up 2 is stored for further use.

[0029]FIG. 2 shows a plan view of the scanning means 7, with theposition of the tip of the pick-up 2 and an electric component 10 to beheld on it being indicated by dashed lines.

[0030] In FIGS. 3 to 9, the sequence of the phases of apicking-and-placing cycle with respect to the scanning means 7 isrepresented.

[0031] According to FIG. 3, the pick-and-place head is located with itspick-up 2 above a component 10 to be picked up and has already beenlowered from its starting position, represented in FIG. 1, to the extentthat its empty underside crosses the scanning beam 22 of the scanningmeans 7. The corresponding position of the pick-up is stored by thecontrol means. It is possible to carry out such scanning after eachchange of pick-up and to compare the standard value ascertained in thisway with the respective measured value when the empty pick-up islowered. Significant deviations may then indicate an error at the tip ofthe pick-up, which for example suggests contaminants or a componentsticking to it.

[0032] According to FIG. 4, the underside of the pick-up 2 is alreadyresting on the component lying in a pocket 11 of a belt 12 and suckingthis component onto it.

[0033] According to FIG. 5, the pick-up 2 has been raised to the extentthat its underside is located above the scanning beam 22 and that thecomponent 10 sucked onto it is interrupting the scanning beam 22. It isalready possible at this moment to establish from the stored value thatthe component to be picked up is present on the pick-up 2.

[0034] According to FIG. 6, the pick-up 2 with the component 10 suckedonto it has just been raised to the extent that the underside of thecomponent 10 clears the scanning beam 22. This change in status isdetected by the control means 6 (FIG. 1), stored with the associatedscanning value of the displacement-measuring means 5. At this moment,the value stored earlier can already be compared with the current value,the difference in height in the lifting position representing a measureof the height of the component 10. If the two scanned values remainunchanged, this means that the component 10 has not being sufficientlysucked onto the pick-up and raised. The control means also knows thecomponent data from a component library. A deviation in the heightvalues may mean that an incorrect type of component has been provided orthat the component was sucked onto the pick-up in an incorrect position.Such components can be removed over a discharge point. The unsuccessfulattempt can trigger a renewed picking-up operation before the pick-upleaves the pick-up position.

[0035] According to FIG. 7, the pick-up 2 has been raised into its uppertransporting position, in which the component 10 is located above thescanning height. The pick-and-place head 1 can now be made to travelinto the placement position for the component 10.

[0036] According to FIG. 8, the pick-up 2 with the component 10 islocated precisely in this placement position above a substrate 13 in thelowering phase. In this case, it can be checked in a way correspondingto FIG. 5 whether the component 10 is still on the pick-up. This check,which may also be combined with a renewed height measurement, permits areliable statement concerning the presence of the component 10. If thelatter has been lost during transport, the pick-up 2 is not lowered anyfurther, so that its tip cannot be contaminated with soldering pastepresent on the substrate 13.

[0037] According to FIG. 9, the component 10 has already been placedonto the substrate 13 and the empty underside of the pick-up 2 has beenraised above the scanning level. During this operation, the status ofthe receiving diode 9 is continuously monitored, so that it can beestablished whether the component has actually been released from thepick-up 2.

[0038] According to FIGS. 9 and 10, another pick-and-place head 14 isdesigned in the manner of a turret and can be made to travel in theworking plane in both coordinate directions x and y. It has a stator 15,on which a rotor 16 can be mounted such that it can rotate step by step.On the rotor, modified pick-ups 17 are arranged such that they protrudein a star-shaped manner and run around in a circular manner. During apicking cycle, in this way all the pick-ups 17 can be loaded withcomponents one after the other in turn before the pick-and-place headtravels over the substrate 13. Along the circulatory path of thepick-ups 17 there is an optical scanning unit 18, with which theunderside of the components 10 can be accurately measured. This meansthat, without a scanning means, the presence and type of the component10 can only be reliably checked in this phase. Consequently, anincorrect pick-up can only be corrected during the next picking cycle.

[0039] Another lift drive 19 with the displacement-measuring means 5 isassigned to a lifting station 20 and is in temporary engagement with theassociated pick-up 17. Another scanning means 21 is fastened to thestator 15 in such a way that the scanning beam 22 is directed just aboveand tangentially in relation to the circulatory path of the components10. By this arrangement it is possible to form the scanning meanslikewise as a forked light barrier with a one-piece bow-like carrier,the base of which is fastened to the stator 15 on one side of thecirculatory path. It is also possible in the case of this pick-and-placehead 14, for scanning steps corresponding to FIGS. 3 to 9 be carriedout.

Patent claims
 1. A method for checking electric components (10) in apick-and-place device for substrates (13), the components (10) beinghandled by a pick-and-place head (1) of the pick-and-place device whichis made to travel in a working plane (x-y), a pick-up (2) for thecomponents (10) being displaced in the pick-and-place head (1)perpendicularly in relation to the working plane (x-y) by means of alift drive (3) between a transporting position and a functioningposition, the component (10) being sucked against an underside of thepick-up (2), the component (10) being raised by the pick-up (2) from apick-up position into the transporting position and, after thepick-and-place head (1) has been made to travel into a placementposition, is lowered onto the substrate (13) into the functioningposition, the positional relationship between the component (10) and thepick-up (2) being checked by an optical scanning means (7) of thepick-and-place head (1), the component (10) being brought by the liftingmovement of the pick-up (2) into the active range of at least onescanning beam (22) of the scanning means (7) oriented transversely inrelation to the lifting direction, in the transporting position, theunderside of the pick-up (2) being located above the scanning beam (22),and the the pick-and-place head (1) having a control means (6), whichchecks the lifting position of the pick-up (2), characterized in thatthe scanning means (7) is coupled to the control means (6), in that thescanning means (7) is activated in a phase before and a phase after thesuction attachment of the component (10), in that the control means (6)detects the presence or absence of the component (10) on the pick-up (2)from the scanning values of the scanning means (7), and in that thecontrol means (6) assesses scanning values remaining the same betweenthe two phases as operating errors.
 2. The method as claimed in claim 1,characterized in that the scanning means (7) is activated during thepicking-up and during the placing of the component (10).
 3. The methodas claimed in claim 1 or 2, characterized in that, in the transportingposition, the underside of the component (10) is raised above the heightlevel of the narrowly focused scanning beam (22), in that, in itsfunctioning position, the underside of the pick-up (2) is displacedunder the height level of the scanning beam (22), in that the lift drive(3) has a displacement-measuring means (5) for determining the liftingposition of the pick-up (2), in that the displacement-measuring means(5) is coupled to the control means (6), in that the lifting means isactivated during the raising and/or lowering of the component (10), andin that the control means (6) ascertains the position in height of theunderside of the component (10) or of the pick-up (2) from the changesin the scanning values during the crossing of the undersides and fromthe respective lifting position of the pick-up (2).
 4. A device forchecking electric components (10) in a pick-and-place device forsubstrates (13), in particular as claimed in one of claims 1 to 3, thepick-and-place device having a pick-and-place head (1) which can be madeto travel in a working plane (x-y) and is intended for handling thecomponents (10), a pick-up (2) for the components (10) being mounted inthe pick-and-place head (1) such that it can be displacedperpendicularly in relation to the working plane (x-y) by means of alift drive (3) between a transporting position and a functioningposition, it being possible for the component (10) to be sucked againstthe underside of the pick-up (2), it being possible for the component(10) to be raised by the pick-up (2) from a pick-up position into thetransporting position and, after the pick-and-place head (1) has beenmade to travel into a placement position, it being possible for it to belowered onto the substrate (13) into the functioning position, thepick-and-place head (1) having an optical scanning means (7) forchecking the component (10) on the pick-up (2) and the scanning means(7) receiving at least one scanning beam (22) which is orientedtransversely in relation to the lifting direction and is narrow in thelifting direction, and in the transporting position, the underside ofthe pick-up (2) being located above the scanning beam (22), thepick-and-place head (1) having a control means (6) for keeping a controlcheck on the lifting movement of the pick-up (2), characterized in thatthe scanning means (7) is coupled to the control means (6), in that thescanning means (7) can be activated in a phase before and a phase afterthe suction attachment of the component (10), in that the control means(6) can detect the presence or absence of the component (10) on thepick-up (2) from the scanning values of the scanning means (7), in thatthe control means (6) assesses scanning values remaining the samebetween the two phases as operating errors.
 5. The device as claimed inclaim 4, characterized in that, in the transporting port position of thecomponent (10), the scanning beam (22) is arranged under the undersideof said component, in that, in its functioning position, the undersideof the pick-up (2) is located underneath the sharply focused scanningbeam (22), in that the lift drive (3) has a displacement-measuring means(5) for determining the lifting position of the pick-up (2), in that thedisplacement-measuring means (5) is coupled to the control means (6), inthat the lifting means can be activated during the raising and/orlowering of the component (10), and in that the control means (6) canascertain the position in height of the underside of the component (10)or of the pick-up (2) from the changes in the scanning values during thecrossing of the undersides and from the respective lifting position ofthe pick-up (2), and from this can calculate the height of the component(10).
 6. The device as claimed in claim 5, characterized in that thescanning means (7) is formed as a forked light barrier with a bow-shapedcarrier for the optical functional parts (for example 8, 9), and in thatthe scanning beam (22) is arranged by deflecting means near theunderside of the scanning means (7) facing the substrate (13).
 7. Thedevice as claimed in claim 4, 5 or 6, characterized in that thepick-and-place head (14) designed in the manner of a turret has a stator(15), on which a rotor (16) is mounted such that it can rotate step bystep, in that the rotor (16) is provided with a multiplicity of pick-ups(17) distributed in a circular manner, in that the pick-up (17) can belowered and raised by the lift drive (19) in a lifting station (20) ofthe pick-and-place head (14), in that the scanning means (31) fastenedto the stator (15) is assigned to the lifting station (20), and in thatthe stator (15) of the pick-and-place head (1) is provided outside thelifting station (20) in addition to the scanning means (7) with anoptics station (18) for ascertaining the position of the component (10)on the pick-up (2).
 8. The device as claimed in claim 7, characterizedin that the scanning beam (22) is oriented in the direction of rotationof the components (10).